#define _USE_MATH_DEFINES
#define _CRT_SECURE_NO_WARNINGS

#include <algorithm>
#include <cmath>
#include <cstdio>
#include <ctime>
#include <deque>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <utility>
#include <vector>
using namespace std;

#define all(x) (x).begin(),(x).end()
typedef long long ll;

typedef vector<int> VI;
typedef vector<string> VS;
typedef vector<VI> VVI;

typedef pair<int,int> PII;
typedef vector<PII> VPII;
#define X first
#define Y second
#define mp make_pair

#define two(x) (1<<(x))
#define twoll(x) ((long long)1<<(x))
#define contain(s,x) (((s)&two(x))!=0)
#define containll(s,x) (((s)&twoll(x))!=0)

#define db(a) cout << #a << "=" << a << " "
#define dbn cout << endl
#define sqr(x) (x)*(x)

string STR(int n) { char tmp[20]; sprintf(tmp,"%d",n); return tmp; }
int INT(string s) { return atoi(s.c_str()); }
template <class Ty, class Tx> Ty to(const Tx &x) { Ty y; stringstream ss; ss<<x; ss>>y; return y; }

const int INF = 1000000007;
const double EPS = 1e-10;

char buf[1<<20];
int TC;

int N,M;

string seq = "ACGT";

int main() {
#define SUBMIT 1
#if !SUBMIT
	freopen("DATA.in", "rt", stdin);
	freopen("DATA.ou", "wt", stdout);
#endif

	gets(buf); TC = atoi(buf);
	
	while (TC--) {
		gets(buf);
		sscanf(buf,"%d%d",&N,&M);
		VS vs;
		for (int i = 0; i < N; ++i) {
			gets(buf);
			vs.push_back(buf);
		}
		int score = 0;
		string res;
//		db(N),db(M),dbn;
		for (int j = 0; j < M; ++j)
		{
			int bst = INF;
			char bstC;
			for (int k = 0; k < 4; ++k) {
				char ch = seq[k];
				int cur = N;
				for (int i = 0; i < N; ++i)
					if (vs[i][j] == ch)
						--cur;
				if (cur < bst)
					bst = cur, bstC = ch;
			}
			score += bst;
			res += bstC;
		}
		printf("%s\n%d\n",res.c_str(),score);
	}

	return 0;
}





